To allow a more rapid determination of heart-type fatty acid-binding protein (FABP) concentration in plasma a direct non-competitive (sandwich-type) ELISA was developed which uses high-affinity monoclonal antibodies to FABP. Total performance time of the one-step immunoassay is 45 min. The standard curve was linear between 0.2-6 micrograms/L, and the within-run and between-run coefficients of variations were below 6 and 11%, respectively. The serum FABP concentration measured in 79 healthy individuals was 1.6 (0.8) [mean (SD), range 0.3-5.0] micrograms/L. The assay can be used for rapid plasma or serum FABP measurement in the early diagnosis of acute myocardial infarction.